COSMO prediction of siloxane compounds absorption on type 3 and type 5 deep eutectic solvents

Abstract

This study reports a Conductor-like Screening MOdel for Real Solvents (COSMO-RS) prediction for 151 type 3 (polar) and type 5 Deep Eutectic Solvents (DES, non-polar) for absorption of hexamethyldisiloxane, octamethyltrisiloxane, hexamethylcyclotrisiloxane, and octamethylcyclotetrasiloxane. Through the examination of generated sigma surfaces, sigma profiles, and sigma potentials, it was found that while the siloxane chains offer sufficiently strong hydrogen bond accepting sites, the steric hindrance of the methyl groups cause less polar solvents (type 5) to outperform the more polar ones (type 3). The thermodynamic study predicts thymol-based type 5 DES as significantly more affinitive for siloxane compounds than common conventional solvents (DEA, MEA, MDEA, menthol, and DPEG Blend) with lnγ activity coefficients reaching low as −0.64. Enthalpy of mixing study shows Vander Waals interactions dominate DES-siloxane compound interactions over hydrogen bonding by over 10x enthalpic release, clarifying discrepancy in literature on how siloxanes are solvated by DES. Thymol: Stearic acid (4:1) showed the lowest excess enthalpy of mixing at −10.4 kcal/mol. An environmental health and safety (EHS) study show the best performing DES components (camphor, capric acid, lauric acid, myristic acid, stearic acid, undecenoic acid, borneol, betaine, hexadecanoic acid, and thymol) are potentially environmentally benign and safe for operation procedures.